Conventional fingerprint sensors include an integrated circuit, such as a silicon die, with an exposed top surface portion for receiving human touch. Due to the exposed top surface, packaging of the integrated circuit can be difficult. For example, conventional packages encapsulate the integrated circuit while exposing a portion of the top surface, but must provide room for wire connections from the top surface to peripheral connection points on a substrate below the integrated circuit. The substrate is provided with additional connection points in order to allow connection of the fingerprint sensor package to a host device. See, U.S. Pat. No. 7,251,351 issued Jul. 31, 2007, to Mathiassen et al. for Sensor Unit, Especially for Fingerprint Sensors; U.S. Pat. No. 6,710,41 issued Mar. 23, 2004, to Chou et al. for Wafer Level Packing of Micro Electromechanical Device.
Some fingerprint sensors provide the silicon die attached to an underside of a flexible substrate, where human touch over the top of the flexible substrate can be sensed indirectly by the silicon die, as discussed in U.S. Pat. No. 7,099,496, issued to Benkley, on Aug. 29, 2006, entitled SWIPED APERTURE CAPACITIVE FINGERPRINT SENSING SYSTEMS AND METHODS, and U.S. Pat. No. 7,751,601, issued on Jul. 6, 2010, to Benkley, entitled FINGER SENSING ASSEMBLIES AND METHODS OF MAKING, both of which are assigned to the assignee of the present application and incorporated by reference. In such fingerprint sensors, the silicon die is either attached directly under the surface to be touched for sensing through the flexible substrate, or attached remote from the surface to be touched and a separate array of metal traces in communication with the silicone die is located directly under the surface to be touched for sensing through the flexible substrate. Rigid substrates or rigid bases must be coupled to the flexible substrate or positioned under the flexible substrate to provide support for the flexible substrate and/or the silicon die when connected to a host device.
Kim et al., “Application of Through Mold Via (TMV) as PoP Base Package,” 2008 Electronic Components and Technology Conference, IEEE (2008) discusses the application of through mold vias (“TMV”) in a “fan-out” wafer level packaging (“WLFO package”) arrangement for a package on package (“PoP”) device. The disclosure of Kim et al. is incorporated by reference.